Rapid prototyping or solid freeform fabrication (“SFF”) is used to form an object having a complex shape without using a mold or die. SFF is used to produce a three-dimensional (“3-D”) object and has been used to create prototypes in a variety of fields, such as the automotive, aerospace, medical, dental and biomedical prostheses manufacturing industries. SFF allows the 3-D object to be produced rapidly and accurately without using a mold or die, which is advantageous because mold processes are expensive and time consuming. While SFF has typically been used to generate prototypes, SFF has also been used to directly produce parts, tools, or molds having precise dimensions and desirable physical properties. Various SFF techniques have been developed, such as stereolithography, selective laser sintering, fused deposition modeling, laminated object manufacturing, and printing techniques. Each of these techniques provides different advantages and disadvantages. For instance, while stereolithography provides 3-D objects that have smooth surface finishes, the technique is slow due to the formation of very thin layers that are cured by a laser. In contrast, a powder-based printing technique is faster but produces 3-D objects that have rough surface finishes. The powder-based printing technique utilizes particles of a powder material to form the 3-D object. However, if the powder particles do not dissolve and if a layer greater than 25 μm is deposited by this printing technique, 3-D objects having very rough surface finishes are produced.
One printing technique uses an inkjet printer to fabricate the 3-D object from thin, two-dimensional (“2-D”) layers. A computer is used to generate cross-sectional patterns of the 2-D layers by storing a digital representation of the object in a computer memory. A computer-aided design (“CAD”) or computer-aided manufacture (“CAM”) software is then used to section the digital representation of the object into multiple, separate 2-D layers. A printer, such as an inkjet printer, is then used to fabricate a layer of material for each layer sectioned by the software. Each of the 2-D layers is formed by applying a powder material on a flat surface or support platform using a roller. The powder material is typically a ceramic, metal, plastic, or composite material. A liquid binder is selectively deposited on the powder material, using a printhead of the inkjet printer, to produce areas of bound powder. Since the liquid binder is only applied to locations where it is needed, the 3-D object is produced faster by printing than by stereolithography. The printing technique is also faster because about 90% of the material is spread in bulk while about 10% of the material is applied by printing. The liquid binder, which is typically a polymeric resin or aqueous composition, is applied in the pattern of the cross-sectional pattern of the 2-D layer. The liquid binder penetrates gaps in the powder material and reacts with the powder particles to create a layer bound in two dimensions. As the reaction proceeds, the binder also bonds each successive 2-D layer to a previously deposited 2-D layer. Additional 2-D layers are formed by repeating the steps of depositing additional powder material and applying the binder solution until the desired number of layers is produced. Since the liquid binder is selectively applied to the powder material, only certain areas of the powder material are bound within the layer and onto the previous layer. After the 3-D object is formed, unbound powder is subsequently removed. One example of a printing technique is known in the art as three-dimensional printing or 3DP™. While 3-D objects have been effectively made by printing, the powder materials and liquid binders that are currently used are problematic. For instance, 3-D objects produced with the powder materials have a rough surface finish due to the particulate nature of the powder materials. In addition, the 3-D objects are typically porous because the powder materials do not pack completely and have limited interactions occurring at the surfaces of the particles. The porous nature and limited surface interaction of the powder materials result in the formation of 3-D objects that have poor mechanical properties. Furthermore, the liquid binder is typically aqueous based, which causes the 3-D object to be sensitive to moisture in the environment and to have reduced environmental robustness. To improve the surface finish, density, mechanical properties, and environmental robustness of the 3-D object, coating or infusion post-treatments have been used. However, these treatments add additional processing steps and cost to the formation of the 3-D object.